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Hybrid phase-locked loop employing analog and digital loop filters

  • US 5,978,425 A
  • Filed: 05/23/1997
  • Issued: 11/02/1999
  • Est. Priority Date: 05/23/1997
  • Status: Expired due to Term
First Claim
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1. A phase-locked loop comprising:

  • a detector;

    a digital loop filter coupled to the detector, the digital loop filter including a digital filter and a successive approximation register which is responsive to the digital filter;

    a digital-to-analog converter coupled to the digital loop filter;

    a variable oscillator coupled to the digital-to-analog converter; and

    an analog filter coupled between the detector and the variable oscillator, wherein the analog filter is enabled when the digital filter is disabled.

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